Board Stiffness Research Articles

Mechanical characterization of visually graded boards from turkish fir and black pine by nondestructive and destructive tests

For the mechanical characterization of Turkish fir and black pine, 400 board specimens with 22 mm× 50 mm × 420 mm were visually graded according to TS 1265 standard. Nondestructive tests were here upon performed using the stress wave method. After specimens were intentionally tested under flatwise bending to research the applicability as an alternative to tension and edgewise bending tests in European strength grading system. According to analyses of variance, the mean values of MOR and MOE differed in four groups at a p<0,05 significance level for visually graded boards. High correlations were found between MOR-MOE (R2=0,837) for fir and MOR-MOE (R2=0,776) for black pine. In addition, correlations of MOR-Knot rate for fir and black pine were respectively R2=0,669 and R2=0,660 showing the effectiveness of flatwise bending tests with the visual grading standard. For nondestructive tests, the mean values of the dynamic modulus of elasticity were very close in between fir and black pine grades while the usage of defect-free density performed better than the density of the whole specimen. Higher strength classes were found for black pine boards (Class 1= C40, Class 2= C27 and Class 3= C22) compared to fir boards (Class 1= C24, Class 2= C22 and Class 3= C18), respectively. Moreover, a simplified nonlinear material model was proposed for numerical modelling, and the results were found in good agreement in terms of the bending stiffness, strength, and deformation capacity of boards especially for class 1 and class 2 in both softwood species.

Structural Properties of Commercial Australian Plantation Hardwood CLT

Significant volumes of plantation hardwood are available in Australia to produce value-added engineered wood products such as cross-laminated timber (CLT). To validate the possibility of utilising this available resource, the bending structural properties of plantation Eucalyptus nitens solid board and finger-jointed feedstock were measured. The studied CLT panels produced from finger-jointed lamellas were subjected to bending strength, bending stiffness, rolling shear strength in bending, and pure rolling shear tests to obtain characteristic design values. Solid and finger-jointed timber test results suggested that boards used in longitudinal lamellas have a bending strength of 36.0 MPa and a modulus of elasticity (MOE) of 13,000 MPa. Finger-jointed timber in crossed lamellas presented a declared bending strength of 25.0 MPa. CLT panels showed a bending strength of 24.0 MPa and a rolling shear strength of 2.0 MPa. The experimental results for the CLT panels evidenced that the CLT bending stiffness matches up very well with the modelled results when an MOE of 13,000 MPa is used to describe the stiffness of longitudinal boards. The results presented in this study establish a basis for the commercial use of Australian plantation hardwood CLT in structural applications such as floors and roofs in commercial and residential buildings.

Study on the Effect of Finger Joints on the Stiffness of Fibre-Managed E. nitens Sawn Boards

Fibre-managed E. nitens has the potential to be used as a feedstock for engineered wood products. This resource, however, has a number of strength-reducing features that need to be removed, and the board needs to be re-joint to be useful in greater lengths for timber construction. A common jointing practice is finger jointing. The suitability of the finger jointing technique for this species is crucial to the mechanical properties of the final product. This study was conducted to explore the influence of finger jointing on the stiffness of sawn boards. A strict manufacturing process of docking and re-joining timber boards in the same location without removing strength-reducing features was conducted to compare the stiffness parameters before and after finger jointing with bending tests. A statistical analysis was conducted. The results showed that the frequency of finger joints along the board did not significantly impact the edgewise stiffness; however, the average flatwise stiffness of the samples with more finger joints was improved slightly. A 10% increase in the end pressure reduced the tip gap significantly but did not influence the stiffness. The finger joint efficiency was 0.824 for the edgewise stiffness of the samples and 1.034 for flatwise stiffness of the jointed sections.

Effect of Stiffening the Printed Circuit Board in the Fatigue Life of the Solder Joint.

Predictive analysis of the life of an electronic package requires a sequence of processes involving: (i) development of a finite element (FE) model, (ii) correlation of the FE model using experimental data, and (iii) development of a local model using the correlated FE model. The life of the critical components is obtained from the local model and is usually compared to the experimental results. Although the specifics of such analyses are available in the literature, a comparison among them and against the same electronic package with different user printed circuit board (PCB) thicknesses does not exist. This study addresses the issues raised during the design phase/life analysis, by considering a particular package with a variable geometric thickness of the user PCB. In this paper, the effect of stiffening the user PCB on the fatigue life of a ball grid array (BGA), SAC305 solder joint is studied. The board stiffness was varied by changing the thickness of the PCB, while the size of the substrate, chips, and solder balls were kept constant. The test vehicle consisted of BGA chips soldered to a user PCB. The thickness of the user PCB was varied, but the surface area of the BGA chip remained identical. The test vehicle was then modeled using a finite element analysis tool (ANSYS). Using a global/local modeling approach, the modal parameters in the simulations were correlated with experimental data. The first resonance frequency dwell test was carried out in ANSYS, and the high-cycle fatigue life was estimated using the stress-life approach. Following the simulation, the test vehicle was subjected to resonance fatigue testing by exciting at the first mode resonance frequency, the mode with the most severe solder joint failure. The resistance of the solder joint during the experiment was monitored using a daisy-chain circuit, and the point of failure was further confirmed using the destructive evaluation technique. Both the experimental and simulation results showed that stiffening the board will significantly increase the fatigue life of the solder joint. Although the amplitude of the acceleration response of the test vehicle will be higher due to board stiffening, the increase in natural frequencies will significantly reduce the amplitude of relative displacement between the PCB and the substrate.

Modeling the tensile mechanical properties of silver birch timber boards

In this paper, the variability of tensile mechanical properties of silver birch timber is investigated and models for the prediction of tension strength and stiffness are developed. Through visual inspections and non-destructive tests, various strength and stiffness related indicators are identified. Destructive tension tests are subsequently performed for the determination of strength and stiffness. On each timber board, strains are measured at four localized regions, whereby, the stiffness of knot sections and clear wood sections are determined. Variability in strength, stiffness, density, knots, grain angle, and annual ring width are investigated along with the relationships between them. A hierarchical model is developed for the prediction of timber board stiffness and the reduction of stiffness due to knots. Models for the prediction of timber board strength and knot cluster strength are developed according to equality and inequality information of the failed specimens, by means of censored regression analysis. Results indicate suitable global and local predictions for silver birch timber, given the dynamic modulus of elasticity, median slope of grain, and knot geometries.

Development of a segregation method to sort fast-grown Eucalyptus nitens (H. Deane & Maiden) Maiden plantation trees and logs for higher quality structural timber products

Key messageA method to segregate trees and logs of planted Eucalyptus nitens (H. Deane & Maiden) Maiden has been developed, showing that accounting for wood quality during the process of segregation and sorting of timber resources allows for the recovery of structural timber of the desired quality.ContextAppropriate sorting of raw forest resources is necessary to allocate logs to different production streams, to ensure that the desired quality of timber is achieved. Acoustic wave velocity can be used to test the wood quality of trees and logs, and its use as a sorting tool needs to be investigated prior to the development of a segregation method to recover high-quality timber.AimsThis study aimed to develop a segregation methodology for plantation E. nitens trees and logs to obtain high-quality structural boards.MethodsForty-nine logs of planted E. nitens were measured, assessed with acoustic wave velocity, and processed into 268 structural boards maintaining board, log, and tree identity. Board stiffness was determined via structural testing and boards were ranked in structural grades. Linear mixed effect models were used to predict board stiffness based on tree and log variables, and machine learning decision trees were used to create a segregation method for board grades. Different segregation options were compared through scenario simulation.ResultsThe prediction of individual board stiffness with tree or log variables yielded low coefficients of variation due to large intra-log variability (R2 = 0.22 for tree variables and R2 = 0.28 for log variables). However, the decision tree identified acoustic wave velocity thresholds to segregate E. nitens trees and logs. When applied in scenario simulation, segregation based on log variables produced the best results, resulting in large shares of high-quality board grades, showing that a segregation method based on wood quality traits can yield larger higher recovery of higher quality timber, in respect to other scenarios.ConclusionAcoustic wave velocity can be used to segregate trees and logs for structural boards from plantation E. nitens, and machine learning decision trees can support the development of a segregation method to determine operational thresholds to increase the recovery of high-quality timber.

Equivalent stiffness of timber used in CLT: closed-form estimates and numerical validation

In this paper, a closed-form approach is presented to estimate rapidly the equivalent stiffness of boards used in cross laminated timber (CLT) panels from local orthotropic behavior at ring scale for varying sawing patterns. It is first assumed that narrow edges are glued. In this case, closed-form Reuss and Voigt bounds are derived for the equivalent layer behavior of CLT. An application to Norway spruce boards is presented and reveals that the cross-layer (rolling) shear behavior lies between 100 and 150 MPa with a careful selection of the board sawing pattern. Then, using finite element method, upper bounds for the cross-layer shear stiffness modulus of boards with and without glued edges are calculated and theoretical predictions are compared with recommendations and experimental data from the literature. Finally, it appears that these bounds remain relevant for CLT layer with unglued narrow edges for common aspect ratios.

Nonsway Model for Lateral Torsional Buckling of Wooden Beams under Wind Uplift

AbstractSimply supported wooden beams nailed to deck boards subjected to wind uplift forces are subjected to compressive stresses at their bottom fibers. Because the restraining action provided by decking is at the top fibers, it is unclear to what extent such restraints are effective in controlling lateral torsional buckling as a possible mode of failure under wind uplift. Present design standards do not have provisions for such cases. Thus, the present study aims to quantify the effect of restraints provided by the deck boards on the lateral torsional buckling capacity of twin-beam-deck systems under wind uplift. Toward this goal, a series of analytical and numerical models were formulated. All models capture the continuous rigid lateral restraint and partial twisting restraint provided by the deck boards. The effects of load type and load position were investigated. The bending stiffness of deck boards was observed to have a significant influence on the lateral torsional buckling capacity of twin-beam-...

Three-dimensional modelling of knots and pith location in Norway spruce boards using tracheid-effect scanning

Knots and the orientation of fibres in timber are decisive for the stiffness and strength of boards. Due to large property variations between members, strength grading is necessary. High resolution ...

Board Stiff TEE

Board Stiff TEE

Board Stiff

Board Stiff

A numerical simulation tool for wood grading model development

Wood is a naturally grown material that has growth irregularities, especially knots and site-related defects. The former result in a pronounced reduction in stiffness and strength of boards. The lack of knowledge regarding the effects of growth irregularities on the mechanical behavior of boards motivated the investigation of such defects by means of physically-based numerical simulations. A model which is based on the combination of the finite element method with sophisticated descriptions of the fiber course and of the material behavior has been developed. Comparisons of model predictions with corresponding experimental results in terms of relations between tensile strength and knot area ratio-values show good agreement and underline the predictive quality of the simulation model. The enhanced insight into the mechanical functionality of a stem–branch junction gained by the newly developed numerical multiscale model might contribute to improve the grading criteria and, thus, to achieve an economic benefit for the wood-processing industry.

Variation in strength, stiffness and related wood properties in young South African-grown Pinus patula

The objective of this study was to examine the variation in and intercorrelation among wood properties determining the suitability of 16- to 20-year-old South African-grown Pinus patula trees for structural timber. A total of 1 112 sawn boards from 340 logs, 170 trees and 17 different compartments were examined. Sawlogs were taken from two height levels from each tree. The mean modulus of elasticity measured on edge (MOEedge) was far below, and the mean twist higher than the limits set for structural grade softwood timber in South Africa. All the desirable properties for structural timber improved with distance from the pith with the exception of the fifth percentile value for modulus of rupture (MOR), which was higher at the pith than for the boards processed adjacent to the pith. Boards processed from the lower part of the stem were superior in most of the important properties compared to the properties higher up in the stem. The correlation between the dynamic modulus of elasticity (MOEdyn) and MOR of boards processed from the logs taken higher up in the stem was much weaker than in the case of the boards processed from the log taken from the lower part in the stem, suggesting that indirect (non-destructive) prediction of MOR decreased in reliability with increase in height in trees. A relatively strong negative correlation was found between the mean growth ring widths of the pith boards and the mean MOEdyn values per compartment, suggesting that slower initial growth in a compartment resulted in increased mean stiffness of boards from that compartment.

Dynamic stability of a human standing on a balance board

The neuromuscular system used to stabilize upright posture in humans is a nonlinear dynamical system with time delays. The analysis of this system is important for improving balance and for early diagnosis of neuromuscular disease. In this work, we study the dynamic coupling between the neuromuscular system and a balance board—an unstable platform often used to improve balance in young athletes, and older or neurologically impaired patients. Using a simple inverted pendulum model of human posture on a balance board, we describe a surprisingly broad range of divergent and oscillatory CoP/CoM responses associated with instabilities of the upright equilibrium. The analysis predicts that a variety of sudden changes in the stability of upright postural equilibrium occurs with slow continuous deterioration in balance board stiffness, neuromuscular gain, and time delay associated with the changes in proprioceptive/vestibular/visual-neuromuscular feedback. The analysis also provides deeper insight into changes in the control of posture that enable stable upright posture on otherwise unstable platforms.

Board Stiff TEE Transesophageal Echocardiography – Second Edition

Board Stiff TEE Transesophageal Echocardiography – Second Edition

Prediction of timber bending strength and in-member cross-sectional stiffness variation on the basis of local wood fibre orientation

Machine strength grading of structural timber is based upon relationships between so called indicating properties (IPs) and bending strength. However, such relationships applied on the market today are rather poor. In this paper, new IPs and a new grading method resulting in more precise strength predictions are presented. The local fibre orientation on face and edge surfaces of wooden boards was identified using high resolution laser scanning. In combination with knowledge regarding basic wood material properties for each investigated board, the grain angle information enabled a calculation of the variation of the local MOE in the longitudinal direction of the boards. By integration over cross-sections along the board, an edgewise bending stiffness profile and a longitudinal stiffness profile, respectively, were calculated. A new IP was defined as the lowest bending stiffness determined along the board. For a sample of 105 boards of Norway spruce of dimension 45 × 145 × 3,600 mm³, a coefficient of determination as high as 0.68–0.71 was achieved between this new IP and bending strength. For the same sample, the coefficient of determination between global MOE, based on the first longitudinal resonance frequency and the board density, and strength was only 0.59. Furthermore, it is shown that improved accuracy when determining the stiffness profiles of boards will lead to even better predictions of bending strength. The results thus motivate both an industrial implementation of the suggested method and further research aiming at more accurately determined board stiffness profiles.

Sorting Eucalyptus nitens plantation logs using acoustic wave velocity

Summary Acoustic wave velocity (AWV) was evaluated as a predictor of wood stiffness in plantation-grown Eucalyptus nitens. To represent the resource currently being directed to the structural timber market, five harvest sites were selected in NE and NW Tasmania spanning two age classes (8 y and 13–15 y) and three productivity classes. A total of 155 sawlogs, 5.5 m long, were cut from 137 harvested trees. AWV was measured in both standing trees and in sawlogs in the mill yard. Disk samples were collected from the butt end of each log to determine green and basic density. Logs were then sawn, and structural boards dried and finished according to commercial processing practice. One sample board per log was then tested for stiffness, bending and shear strength and hardness. Sites differed significantly (P < 0.001) in standing tree AWV, log AWV and all wood properties of the butt logs, with the 13–15-y age class displaying higher AWV, wood basic density, stiffness and hardness than the 8-y age class. Log AWV2 explained 54% of the variance in board static modulus of elasticity (MoEstat) for the pooled data. At the age class level, 47% of the variance was explained for the 13–15-y logs, but the correlation was much poorer—explaining only 6% of variance in MoEstat—for the subset of 56 logs from the two 8-y-old sites. Dynamic MOE (MoEdyn, the product of green density and log AWV2), gave useful predictions of MoEstat for the younger age class. MoEdyn calculated using log AWV2 explained 56% of the variation in MoEstat, facilitating the segregation of logs into three stiffness classes. Tree AWV2 explained 40% of the variation in MoEstat for the pooled data, similarly enabling segregation of boards into three stiffness classes. Relative to segregation at the log level, a similar percentage of low-stiffness material was identified; but ability to identify higher-stiffness material was reduced. A significant (P < 0.01) positive correlation of 0.30 was found between board stiffness and hardness, indicating that segregation based on increasing stiffness would also improve hardness.

Strength grading of narrow dimension Norway spruce side boards in the wet state using first axial resonance frequency

Strength grading of Norway spruce [Picea abies (L.) Karst.] side boards in the wet state was investigated. For a sample of 58 boards, density and dynamic modulus of elasticity in the axial direction (MOEdyn) were determined in the wet state. The boards were then split into two parts and the procedure of determining MOEdyn was repeated both before and after the boards were dried to a target moisture content of 12%. Finally, tensile strength of the split boards was measured and its relationship to MOEdyn for both wet and dried split boards was determined. The investigation also included an evaluation of a so called reversed lamination effect on the stiffness caused by the splitting of boards into two parts. The results show that strength grading of split boards in the wet state can give just as good results as grading performed after drying. The reversed lamination effect on the stiffness of split boards was found to be of lower order.

The Structured Oral Examination in Clinical Anaesthesia

This is a book written by British authors to assist United Kingdom anesthesia registrars in preparing for their oral board examination in the specialty. It is not specifically designed for the American Board of Anesthesiology (ABA), but rather is a generic guide to important information for ABA oral board preparation. Although there are no stem questions or new format questions to study (unlike the popular oral board preparation book entitled Board Stiff), this book does have significant value as a study guide for the oral board examination. The Structured Oral Examination in Clinical Anaesthesia: PracticeExamination Papers consists of 10 complete sets of structured oral examinations. Each set is subdivided into 2 sections, clinical anesthesia and clinical science. Each clinical anesthesia section is composed of 1 long and 3 short cases, and relevant clinical information for each long case is presented. Each clinical science case is composed of 4 key topics: applied anatomy, physiology, pharmacology, and physics of equipment used in anesthesia practice. This book is designed to assist the reader in making rational decisions when discussing various case scenarios. Most importantly, the reader is shown how to assess their knowledge and provide answers that they can defend. Each structured oral examination long case is composed of a scenario, relevant material such as history, clinical presentation, laboratory results, electrocardiograms, chest radiographs, echocardiographic findings, pulmonary function test results, and a series of questions and answers. Each question provides the reader with answers organized by organ system. At the end of each long case scenario, key points and further reading materials are provided. Each long case is followed by 3 short cases that are composed of a short scenario with a series of questions, answers, key points, and a reading list to provide readers with additional breadth and depth of information related to the topic. The short cases reviewed represent more diversified topics that also appear regularly on the examination (e.g., emergency cesarean delivery, head injury, myasthenia gravis, latex allergy, and acute and chronic pain issues). The long cases provide the reader with helpful hints, updates, and key points on how to manage various clinical scenarios. Answers are provided for all questions at the end of each long case. Although this book contains a unique combination of information, it does not describe the format of the ABA oral board examination. The Structured Oral Examination in Clinical Anaesthesia is organized in a perioperative (i.e., pre-, intra-, and postoperative) format and provides enough specifics to be a valuable oral board preparation tool. A critical review of actual oral examination scenarios would be a useful addition to the book. In addition, reorganizing the 10 cases into a stem question format (i.e., question and answer) would be helpful to the candidate preparing for the ABA oral board examination. In summary, this book is a useful study guide for anesthesia trainees in the oral board preparation process. The book contains much useful review information, and more importantly, explains how to proceed with a differential diagnosis, with in-depth discussions of likely causes, diagnostic procedures, and treatment modalities. Reviewing specific clinical scenarios, specific questions, and appropriate responses should facilitate the examinee's learning curve in preparing for their oral board examination. Our major criticism of this book relates to the fact that it is not written as an ABA oral board preparation book in contrast to Board Stiff. However, it does provide more useful academic material than Board Stiff and is a useful study guide for the oral examination. Roya Yumul, MD, PhD Ronald H. Wender, MD Department of Anesthesiology Cedars-Sinai Medical Center Los Angeles, California [email protected]

Stiffness and checking of Eucalyptus nitens sawn boards: genetic variation and potential for genetic improvement

A trial was undertaken to assess the extent to which variation in sawn-board quality traits of plantation-grown Eucalyptus nitens is under genetic control and amenable to genetic improvement. Five hundred and sixty trees from 129 families and three central Victorian races were sampled from an open-pollinated progeny trial in Tasmania, Australia. Acoustic wave velocity (AWV) was assessed on standing-trees and sawlogs. Wedges from disks extracted from sawlogs were assessed for basic density and checking. Processed boards from 496 of the trees were assessed for board stiffness (static modulus of elasticity, MOE), and internal and surface checking. Genetic differences among races were significant for AWV and MOE traits. The Southern race had the highest mean values for these traits. Significant additive genetic variation within races was observed in all traits, demonstrating that the quality of plantation-grown E. nitens boards could be improved through breeding. Estimated narrow-sense heritabilities were 0.85 for standing-tree AWV, 0.71 for log AWV, 0.37 for board MOE, and ranged from 0.20 to 0.52 for checking traits. A strongly positive genetic correlation (rg = 1.05) was observed between standing-tree AWV and board MOE, indicating that AWV could be used as a selection trait to improve E. nitens board stiffness. The genetic correlation between basic density and board MOE was also positive (rg = 0.62). However, a significant and adverse genetic correlation (rg = 0.61) was identified between basic density and surface check length. Wood stiffness and checking traits were more-or-less genetically independent, and genetic correlations between surface and internal checking were positive but only moderate (rg = 0.48-0.52).